The invention relates to a rope pulley construction comprising a frame, at least one rope pulley equipped with a rope groove, rope pulley bearing, guard to prevent a lifting rope from coming off the rope pulley, and suspension point.
Publication DE-3 405 759 discloses a rope pulley construction comprising at least one rope pulley, side casings attached on both sides of the rope pulley to a hollow bearing shaft, and a flexible fixing part for hanging the rope pulley construction. Circularly symmetrical openings are arranged in the side casings at a bearing shaft. A fixing mechanism is drawn through the hollow bearing shaft and the openings in the side supports, the openings being shaped to support the flexible fixing part. The rope pulley construction disclosed in the publication further comprises a separate guard arranged on top of the rope pulley to prevent a lifting rope from coming off the rope pulley, and side plates supporting the fixing part arranged on both sides of the construction. Fixing screws are used for assembling the rope pulley construction. A drawback of the rope pulley construction disclosed in the publication is that the construction is complex, comprising a great number of parts, which increases costs and assembly time.
A characteristic of the known rope pulleys is that when the rope winds onto the rope pulley, a sector formed by the contact area is then smaller than half the rim of the rope pulley. Consequently, the point of application of the resultant force of the rope force is located below the rope pulley center in a hook block, for example. If the shaft of the hook block is hung at the center of the rope pulley, the result is a labile construction, which is emphasized particularly with zero load when the weight of the hook block itself is small. Attempts have been made to eliminate the problem with balance by fixing the shaft of the hook block below the rope pulley, but then the height of the hook block increases too much at the expense of the lifting height. Another alternative is to hang the hook block lower by a separate suspension piece, which, however, increases the weight and number of parts of the construction.
An object of the present invention is to provide a rope pulley construction which has a simple structure and which can be suspended in a preferred manner.
A rope pulley construction of the invention is characterized in that the frame comprises two plate parts joined together such that the joined plate parts provide suspension for the rope pulley, at least one suspension point and guard to prevent the lifting rope from coming off the rope pulley.
The idea underlying the invention is that in a rope pulley construction comprising a frame, at least one rope pulley and its bearing, guard to prevent a lifting rope from coming off the rope pulley, and suspension point for hanging the rope pulley, the frame comprises two plate parts joined together to simultaneously provide suspension for the rope pulley, at least one suspension point for fixing the rope pulley construction on a hook block, for example, and guard to prevent a lifting rope from coming off the rope pulley. According to a preferred embodiment of the invention, the joined plate parts are identical. According to a second preferred embodiment of the invention, the rope pulley is implemented as a rope groove ring wherein the rope pulley and the bearing are combined such that the rope groove is arranged directly on the outer rim of the bearing. According to a third preferred embodiment of the invention, the suspension point of the rope pulley construction is located asymmetrically with respect to the center of the rope pulley.
The rope pulley construction described in the invention is simple, comprising only few parts, which means that the construction is lightweight. The two parts joined together provide the suspension for the rope pulley, suspension point for supporting the suspension shaft, and guard to prevent a lifting rope from coming off the rope pulley. Being identical, the plate parts are cost-efficient to manufacture. Furthermore, the rope pulley construction is quick and simple to assemble. The suspension of the suspension shaft is also stable since the location of the suspension shaft can be chosen with respect to the location of the resultant of the rope force. Furthermore, in the rope pulley construction of the invention, the outside diameter of the bearing can be increased to almost equal the winding diameter of the lifting rope, which enables a reliable and long-run bearing to be achieved.